The present invention relates to a flat key and lock therefor. More particularly this invention concerns a high-security lock using a flat key.
A standard flat-key lock has a cylinder or barrel in which a plug can rotate about an axis. The plug is formed with an axially extending hole to which the key is fitted. Tumblers are displaceable transversely of the axis between freeing positions blocking rotation of the plug in the barrel and locking positions permitting such rotation. The key has an edge formed with bits that engage the respective tumblers when it is fully inserted in the hole to set the tumblers in the freeing positions.
European 851,079 describes a key that engages split tumbler pins. The butting thus forms a sort of cam. In addition the rear edge of the key is provided on one side with a cam for additional tumblers. This combination of conventional tumbler pins and the additional tumbler is however disadvantageous since the number of possible codings is limited.
It is therefore an object of the present invention to provide an improved flat key and lock therefor.
Another object is the provision of such an improved flat key and lock therefor which overcomes the above-given disadvantages, that is which is of simple construction in that it is made of a small number of standard parts so that it can be made inexpensively yet which offers a large number of codings so that it is very secure against both picking and forcing.
A flat key has according to the invention a flat blade extending along an axis and having an axially extending edge formed to each side of a central axially extending key plane with a pair of axially extending inner edge surfaces flanking the key plane and each formed with a plurality of bits offset transversely at different spacings from the axis. The bits on one side of the key plane are offset axially to the bits on the other side of the key plane.
This system greatly increases the number of bits that are available, making the potential codings or combination vast. The offset makes a lock for this key still relatively short.
The key edge is formed according to the invention with a pair of outer edge surfaces flanking the inner edge surfaces and each formed with a plurality of bits offset transversely at different spacings from the axis. The bits of the outer edge surface on one side of the key plane are offset axially to the bits of the outer edge surface on the other side of the key plane. Furthermore blade can have a side face formed with a longitudinal actuating formation. In addition the key can be reversible when it has a second axially extending edge formed identically to the first-mentioned edge.
A lock has according to the invention a flat key having a flat blade extending along a key axis and having an axially extending edge formed to each side of a central axially extending key plane with a pair of axially extending inner edge surfaces flanking the key plane and each formed with a plurality of bits offset transversely at different spacings from the key axis. The bits on one side of the key plane are offset axially to the bits on the other side of the key plane as described above. A barrel having an inner surface centered on a lock axis holds a plug rotatable about the lock axis in the barrel, bisected by a plug plane including the lock axis, and formed with an axially extending and open key hole adapted to receive the key with the axes coaxial and the planes coplanar. A respective set of axially spaced tumblers is displaceable in the plug to each side of the plug plane parallel to the plug plane. The tumblers of one of the sets engage the key in the hole at locations offset axially from the tumblers of the other sets. Respective springs urge the tumblers radially outward.
The inner edge surface is formed to each side of the plug with a radially inwardly directed retaining notch and each tumbler is formed with a radially outwardly directed retaining notch. The lock further has according to the invention respective retaining elements in the plug to each side of the plug plane and each having an outer end engageable in the respective inner-surface retaining notch and inner bus engageable in the notches of the tumblers on the respective side of the plug plane. Each of the retaining elements is an axially elongated bar and each of the respective grooves is axially elongated. Springs urge the retaining elements radially outward.
The retaining-element outer ends are both offset to the same side of a secondary plane through the lock axis and transverse to the plug plane. The grooves are similarly offset so that the elements can only both fit in the respective grooves in a predetermined angular position of the plug in the barrel. The key can only be withdrawn when the tumblers are clear of the retaining elements since these tumblers must move parallel to the key plane as the key is inserted or withdrawn. In a system with two such radially outwardly directed retaining notches there are two positions in which the key can be withdrawn.
The tumblers in accordance with the invention on one side of the plane are offset to the tumblers on the other side of the plane by a distance equal to about 25% of an axial spacing between adjacent tumblers on the same side of the plane.
The key edge can also be formed with a pair of outer edge surfaces flanking the inner edge surfaces and each formed with a plurality of bits offset transversely at different spacings from the axis. The bits of the outer edge surface on one side of the plane are also offset axially to the bits of the outer edge surface on the other side of the plane. The tumblers have key-engaging bumps some of which are relatively long and engage the respective inner edge surface and the others of which are short and engage the respective outer edge surface. At least one of the long bumps is undercut or J-shaped so as to pass the respective outer edge surface.
The plug according to the invention is formed with respective guides in which the tumblers are displaceable and immediately adjacent each guide and parallel thereto with respective spring bores holding the respective tumbler springs, each tumbler having a protecting extending laterally into the respective spring bore. The guides are of rectangular section.